Method for restoring function of plasma display panel and plasma display panel

ABSTRACT

A method for restoring the function of a plasma display panel according to the present invention restores a function of a plasma display panel by raising the temperature of the plasma display panel to 400° C. to 800° C.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a plasma display panel (PDP) and amethod for restoring the function of a PDP, when it becomesdeteriorated, the PDP being capable of being used as the display ofwall-hanging color televisions and variety of other information displaydevices for the reason that PDP is inexpensive to produce and is thinwith a large, high-resolution screen.

(2) Description of the Related Art

Plasma display panels (hereinafter referred to also as PDP(s)) areroughly categorized into AC type and DC type in terms of their drivemethods, whereas they are roughly divided into surface discharge typeand counter discharge type in terms of their discharge methods.Nowadays, AC surface discharge PDPs are in the mainstream because PDPsof this type can have a high-definition screen and allow for easy andsimple production. An attempt has been made to improve viewability andcolor reproducibility of the PDPs by increasing the luminance of displaythat utilizes phosphors.

For example, conventional PDPs include a technology in which phosphorlayers are composed of a large number of granular phosphors, each beingcoated with a thin film made of translucent material whose refractiveindex is smaller than that of the phosphors (see Japanese Laid-OpenPatent publication No. 7-320645). This conventional PDP is capable ofproducing the following effects: the display luminance is increasedthanks to the improvement in the excitation efficiency, which isattributable to the fact that the reflection at the surface layer of thephosphors is reduced and that the transmittance of ultraviolet (UV)light into the phosphors is increased; and the decay of the phosphorscan be prevented because the thin-films protect the phosphors from ionsat the time of plasma discharge.

Meanwhile, as AC-driven PDP, which uses a magnesium oxide film as adielectric protective film, a PDP is known that prevents the degradationof electric characteristics by forming, on the magnesium oxide film, ananti-gas-absorbing film having insulating property and visible-lighttransmission property so as to prevent the magnesium oxide film fromabsorbing gas at the fabrication stage (see Japanese Laid-Open Patentpublication No. 2000-348626). Since this PDP is capable of reducing thegas absorption of magnesium oxide as well as reducing the breakdownvoltage by successively forming an anti-gas-absorbing film on themagnesium oxide film, it is possible to achieve the enhanced stabilityand improved performance of discharge.

Furthermore, there has been proposed a PDP fabrication method thatincludes a process in which: electrodes, which are formed on at leastone of a pair of glass substrates, are covered with a dielectric layer;a protective layer for protecting such dielectric layer from dischargeand a temporary protective film for temporarily protecting the surfaceof such protective film up until the panel assembling process, areformed on the surface of such dielectric layer; after said one glasssubstrate and the other substrate are assembled into a panel, thetemporary protective film is removed by generating plasma in the panel(see Japanese Patent No. 3073451). In this fabrication method, since thetemporary protective film is successively formed on the protective filmafter such protective film is formed, no affected layer is formed on thesurface of the protective film. Accordingly, it becomes possible for theplasma display panel to have a protective film with excellent dischargeproperties.

Meanwhile, it is known that wavelength shift and luminance degradationof phosphors occur when a PDP is sealed in the fabrication andassembling processes or after being used for a long period of time as aproduct. Such wavelength shift and luminance degradation are especiallynotable in blue phosphors out of the three color phosphors. In the caseof wavelength shift, discoloration of luminescent colors occurs, whereasin the case of luminance degradation, luminescence intensity is reduced,both of which lead to the deterioration in display function.

Such deterioration in the display function of PDPs is assumed to occurbecause of one of the following factors: wavelength shift that occursdue to the OH group being bound to BAM (blue phosphor: an abbreviationof BaMgAl₁₀O₁₇) as a result of oxygen defect and luminance degradationdue to the oxidization of EU²⁺; and destruction of BAM structure due to(UV) light, i.e., due to lowered crystallinity. However, no proposal hasbeen made about means for restoring a deteriorated display function ofPDPs attributable to the above wavelength shift and luminancedegradation.

The present invention has been conceived in view of the aboveconventional problem, and it is an object of the present invention toprovide a method for restoring the function of a plasma display panelthat can efficiently restore the display function of a plasma displaypanel when its display function is deteriorated due to wavelength shiftand luminance degradation of phosphors, as well as to provide a plasmadisplay panel that is equipped with means for efficiently restoring itsdeteriorated display function.

SUMMARY OF THE INVENTION

In order to achieve the above object, the method for restoring thefunction of a plasma display panel of the invention according to claim 1is characterized in that it comprises restoring a function of a PDP byraising a temperature of at least a phosphor layer in the PDP to 400° C.to 800° C.

The invention according to claim 2 is characterized in that, in themethod for restoring the function of a PDP according to claim 1, the PDPis equipped with a heating element, and the temperature of at least thephosphor layer in the PDP is raised to 400° C. to 800° C. by energizingthe heating element.

The method for restoring the function of a plasma display panel of theinvention according to claim 3 is characterized in that it comprisesrestoring a function of a PDP by raising a temperature of a phosphorlayer in the PDP to 400° C. to 800° C. through irradiation of light tothe PDP.

The invention according to claim 4 is characterized in that, in themethod for restoring the function of a PDP according to claim 3, thelight is irradiated to the phosphor layer from outside the PDP through aglass substrate and a dielectric layer in the PDP.

The method for restoring the function of a plasma display panel of theinvention according to claim 5 is characterized in that it comprisesrestoring a PDP by raising a temperature of a phosphor layer in the PDPto 400° C. to 800° C. by inductively heating conductive particlesthrough application of a high-frequency electric field to the PDP, saidconductive particles being mixed, at a predetermined ratio, withphosphor particles that make up the phosphor layer.

The method for restoring the function of a plasma display panel of theinvention according to claim 6 is characterized in that it comprisesrestoring a PDP by raising a temperature of a phosphor layer in the PDPto 400° C. to 800° C. by inductively heating dielectric particlesthrough application of a high-frequency electric field to the PDP, saiddielectric particles being mixed, at a predetermined ratio, withphosphor particles that make up the phosphor layer.

The plasma display panel of the invention according to claim 7 ischaracterized in that it comprises: a first substrate on which dischargeelectrodes and a first dielectric layer are formed, each of saiddischarge electrodes generating a display discharge and said firstdielectric layer covering the discharge electrodes; and a secondsubstrate on which the following are formed: address electrodes that arelocated orthogonally to the discharge electrodes; a second dielectriclayer that covers the address electrodes; barrier ribs that are formedon the second dielectric layer; phosphor layers, each being formed in aconcave portion between each two neighboring barrier ribs; and heatingelements that are located close to the respective phosphor layers.

The invention according to claim 8 is characterized in that the heatingelements according to claim 7 have a linear shape and are formed on thesecond substrate, each of the heating elements being located betweeneach two neighboring address electrodes in parallel with said addresselectrodes and being embedded in the second dielectric layer.

The invention according to claim 9 is characterized in that the heatingelements according to claim 7 have a linear shape and are located abovethe respective address electrodes in parallel with said addresselectrodes, the heating elements being embedded in the second dielectriclayer.

The invention according to claim 10 is characterized in that, in the PDPaccording to claim 7, each of the heating elements is formed at least aspart of each of the barrier ribs.

The invention according to claim 11 is characterized in that the PDPaccording to claim 7 further comprises: a control drive circuit thatcontrols drive of the discharge electrodes and the address electrodes;and a heating element energization circuit that controls energization ofthe heating elements so that said heating elements heat the phosphorlayers at a predetermined temperature for a predetermined time.

The invention according to claim 12 is characterized in that the PDPaccording to claim 7 further comprises: a timer circuit that measures apanel drive time during which the PDP has been driven; a memory thatstores a total drive time that is obtained by accumulating each paneldrive time measured by the timer circuit, said total drive time beingupdated and stored into the memory every time the timer circuit newlymeasures a panel drive time; a function restoration key by which aninstruction for energizing the heating element is inputted, said keybeing operated manually; a heating element energization circuit thatenergizes the heating elements when the function restoration key isoperated; and a control unit operable to indicate that an operation ofthe function restoration key should be performed, when judging that thetotal drive time stored in the memory reaches a set time.

The invention according to claim 13 is characterized in that the PDPaccording to claim 7 further comprises: a timer circuit that measures apanel drive time during which the PDP has been driven; a memory thatstores a total drive time that is obtained by accumulating each paneldrive time measured by the timer circuit, said total drive time beingupdated and stored into the memory every time the timer circuit newlymeasures a panel drive time; a heating element energization circuit thatenergizes the heating elements; and a control unit operable to directthe heating element energization circuit to energize the heatingelements when judging that the total drive time stored in the memoryreaches a set time.

The invention according to claim 14 is characterized in that the PDPaccording to claim 13 further comprises a clock circuit that providestime information, wherein when a pre-set time is reached, the controlunit directs the heating element energization circuit to energize theheating elements, based on the time information provided by the clockcircuit.

The invention according to claim 15 is characterized in that in the PDPaccording to claim 11, the heating element energization circuit controlsthe energization of the heating element so that the phosphor layers areheated at 400° C. to 800° C., preferably 500° C. to 600° C., for 10 to120 minutes, preferably 20 to 60 minutes.

The disclosure of Japanese Patent Application No. 2003-388616 filed onNov. 19, 2003 and the disclosure of Japanese Patent Application No.2004-161925 filed on May 31, 2004 including specification, drawings andclaims are incorporated herein by reference in its entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, advantages and features of the invention willbecome apparent from the following description thereof taken inconjunction with the accompanying drawings that illustrate a specificembodiment of the invention. In the Drawings:

FIG. 1 is a cutaway perspective view showing a plasma display panel(PDP) according to a first embodiment of the present invention;

FIG. 2 is a cross-sectional diagram of the PDP along the line A-A shownin FIG. 1;

FIG. 3 is a cross-sectional diagram of the PDP along the line B-B shownin FIG. 1;

FIG. 4 is a block diagram showing an electric system of the PDP;

FIG. 5 is a flowchart showing control processing for restoring displayfunction of the PDP;

FIG. 6A is a flowchart showing a process of fabricating a frontstructure;

FIG. 6B is a flowchart showing a process of fabricating a rearstructure;

FIG. 6C is a flowchart showing a process of assembling the frontstructure and the rear structure;

FIGS. 7A, 7B, and 7C are diagrams, each showing a different pattern offorming heating elements on the PDP;

FIG. 8 is a cross-sectional diagram showing a PDP according to a secondembodiment of the present invention;

FIG. 9 is a cross-sectional diagram showing a PDP according to a thirdembodiment of the present invention;

FIG. 10 is a flowchart showing processing of fabricating the rearstructure of the PDP according to the second embodiment;

FIG. 11 is a flowchart showing another control processing for functionrestoration according to each of the aforementioned embodiments;

FIG. 12 is a flowchart showing a first method for restoring the functionof a PDP according to the present invention;

FIG. 13 is a schematic diagram showing a second method for restoring thefunction of a PDP according to the present invention;

FIG. 14 is a schematic diagram showing a variation of the second methodfor restoring the function of a PDP;

FIG. 15 is a schematic diagram showing a third method for restoring thefunction of a PDP according to the present invention; and

FIG. 16 is a schematic diagram showing a fourth method for restoring thefunction of a PDP according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following describes the preferred embodiments of the presentinvention with reference to the drawings.

First Embodiment

FIG. 1 is a cutaway perspective view showing a plasma display panel(PDP) 100 according to the first embodiment of the present invention,FIG. 2 is a cross-sectional diagram of the PDP 100 along the line A-Ashown in FIG. 1, and FIG. 3 is a cross-sectional diagram of the PDP 100along the line B-B shown in FIG. 1.

In FIGS. 1 to 3, a front glass substrate 1 is made of a heat-resistantglass for PDP such as soda glass substrate and high-distortion pointglass substrate. On one of the surfaces of the front glass substrate 1(the undersurface in FIG. 1/FIG. 3), a plurality of discharge electrodes4, each being comprised of a pair of a scan electrode 2 and a sustainelectrode 3 which are made of silver or Cr—Cu—Cr and which are placed inparallel and opposite each other. Between each two neighboring dischargeelectrodes 4, a light-shielding layer 5 is formed. Each scan electrode 2and each sustain electrode 3 are respectively made of a transparentelectrode 2 a and a transparent electrode 3 a, as well as of a buselectrode 2 b and a bus electrode 3 b such as silver that areelectrically connected to the transparent electrodes 2 a and 3 a,respectively.

Furthermore, the above plurality of discharge electrodes 4 are coveredwith a dielectric layer 6 that is formed on one surface of the frontglass substrate 1. Moreover, a protective film 7 made of MgO is formedon one surface of the dielectric layer 6. This protective film 7 servesalso as a secondary electron emission film.

Meanwhile, a rear glass substrate 8, which is also made of aheat-resistant glass for PDP such as soda glass substrate andhigh-distortion point glass substrate as in the case of the front glasssubstrate 1, is placed in parallel and facing one surface of the frontglass substrate 1. On the surface of this rear glass substrate 8 thatfaces the front glass substrate 1, address electrodes 10 are formedorthogonally to the discharge electrodes 4, each being comprised of ascan electrode 2 and a sustain electrode 3. Between each two neighboringaddress electrodes 10, a heating element 11 is placed in parallel withthe address electrodes 10. Each heating element 11, which is made of ahigh-resistivity material such as stainless, nichrome, tungsten, andmolybdenum, is formed in a linear form. When power is applied, eachheating element 11 generates heat so as to restore the deteriorateddisplay function. Detailed descriptions of heating elements 11 are givenlater.

The above-described address electrodes 10 and heating elements 11 arecovered with a dielectric layer 9 that is on the rear glass substrate 8.On this dielectric layer 9, a plurality of striped barrier ribs 12 areformed above the respective heating elements 11 in parallel with suchheating elements 11 and the address electrodes 10. A phosphor layer 13is formed on the outer surface of each barrier rib 12 as well as on thesurface of the dielectric layer 9. Each of the above dielectric layers 6and 9 is an electrical insulating material that serves as a capacitorstoring electric charge.

The front glass substrate 1 and rear glass substrate 8, which are placedfacing each other with a predetermined gap between them, are sealedaround them, as a result of which a small discharge space is createdinside such sealed two substrates. Thus, the scan electrodes 2 andsustain electrodes 3, and the address electrodes 10 are placedorthogonally to each other across such small discharge space. Thisdischarge space is filled, as discharge gas, with one of helium, neon,argon, and xenon, or a mixture of two or more of such gases.Furthermore, as FIG. 2 shows, the discharge space is divided by thebarrier ribs 12 into a plurality of display spaces, and an intersectionpart of each discharge electrode 4 and address electrode 10 facing eachother across each display space, forms a discharge cell 14. In eachdischarge cell 14, red, blue, and green phosphor layers 13 aresuccessively deposited on a color-by-color basis. A gap between each ofthe discharge cells 14 is covered with a light-shielding layer 5, sothat no discharges outside the discharge cells can be visible fromoutside.

A heat insulation material 17 is provided on a surface of the rear glasssubstrate 8 that is in the opposite direction to the front glasssubstrate 1. Inside this heat insulation material 17, as shown in FIG.2, a plurality of beams 17 a create a plurality of vacuum insulationspaces 17 b. This heat insulation material 17 prevents heat generated bythe heating elements 11 from emitting to outside from the surface of therear glass substrate 8 that is in the opposite direction to the frontglass substrate 1.

FIG. 4 is a block diagram showing the electric system of the PDP 100. Aplurality of methods are available as a method for driving the PDP 100,but since the present invention is applicable to any of such methods,only a typical drive method is described in the present embodiment.

When the PDP 100 is driven, a display control circuit 18 supplies commonsustain voltage to all the discharge cells 14 via a sustain voltagesupply circuit 19. When the control unit 20 specifies, to the displaycontrol circuit 18, each discharge cell 14 to be driven, the displaycontrol circuit 18 selects, via an X address circuit 21 and a Y addresscircuit 22, an address electrode 10 and a discharge electrode 4corresponding to each discharge cell 14 specified by the control unit 20from among a plurality of discharge cells 14, and energizes suchselected address electrode 10 and discharge electrode 4. Accordingly, ineach selected discharge cell 14, a small writing discharge first occursbetween the scan electrode 2 and the sustain electrode 3, as a result ofwhich a wall charge is formed. Using this wall charge, a main dischargeoccurs between two neighboring discharge electrodes 4, and UV light thatis generated by such main discharge is then emitted to the phosphorlayers 13. Accordingly, a color image is displayed on the PDP 100.

When a total drive time of the PDP 100 reaches 2000 to 3000 hours, forexample, its display function becomes slightly deteriorated in the formof wavelength shift and luminance degradation especially in the bluephosphors out of the phosphor layers 13 of each color. In view of this,the present embodiment is equipped with a function of restoring thedeteriorated display function, when the above total drive time isreached, by presenting a screen display that prompts a user to carry outan operation for restoring the display function and then by energizingthe heating elements 11 if such user has carried out the restorationoperation as prompted by the screen display. Here, screen display isonly an example, and therefore other means such as lamp and alarm may beused to notify the user that an operation for restoring the displayfunction should be performed.

As the constituent elements for restoring the display function, the PDP10 is equipped with: a heating element energization circuit 23 thatenergizes the heating elements 11 by supplying power to them in responseto an instruction from the control unit 20; a timer circuit 24 thatmeasures a total drive time; a memory 27 that stores the total drivetime measured by the timer circuit 24; a power detection circuit 28 thatdetects whether or not the PDP 100 is powered on; a function restorationkey 30 that gives an instruction, when it is operated, that processingfor restoring the display function should be performed; and an interlockcircuit 29 that locks the function restoration key 30 so that thefunction restoration key 30 cannot be operated, when the power detectioncircuit 28 detects that the PDP 100 is powered on.

Next, referring to a flowchart of FIG. 5, a description is given ofcontrol processing for restoring the display function. The control unit20 continuously monitors whether the power of the PDP 100 is on or not,i.e., whether the PDP 100 is in the driven state or not, based on thepresence/absence of a power-on signal inputted from the power detectioncircuit 28 (Step S1). Every time there is an input of power-on signal,the control unit 20 causes the timer circuit 24 to start a timemeasuring operation (Step S2). Then, the control unit 20 monitors if apower-on signal will stop being inputted as a result of terminating thedrive of the PDP 100 (Step S3). When judging that the PDP 100 has beenpowered off and no power-on signal is inputted any more, the controlunit 20 obtains a new total drive time by adding the total drive timeread from the memory 27 to the drive time measured by the timer circuit24 (Step S4), and judges whether such obtained total drive time exceedsa predetermined time or not (Step S5). Here, as the predetermined time,2000 to 3000 hours is set after which processing for restoring thedisplay function is required to be performed.

When judging that the predetermined time is not exceeded, the controlunit 20 updates the memory 27 by storing a newly obtained total drivetime (Step S6), after which the control unit 20 returns to Step S1 torepeat the above control processing. Meanwhile, when judging that thepredetermined time is exceeded (Step S5), the control unit 20 directsthe display control circuit 18 to present a screen display that promptsthe user to operate the function restoration key 30 (Step S7).Accordingly, the display screen shows a message saying, for example, asfollows: “Display function restoration processing is required now. Pressfunction restoration key after turning off the power.”

Then, the control unit 20 first monitors whether or not the user haspowered off the PDP 100 as promoted by the screen display, on the basisof the presence/absence of a power-on signal from the power detectioncircuit 28 (Step S8), and when judging that the PDP 100 has been poweredoff, directs the interlock circuit 29 to unlock the function restorationkey 30 (Step S9). Stated another way, the function restoration key 30 isusually locked by the interlock circuit 29 so that the key 30 cannot beoperated. This aims at preventing the occurrence of inconveniences to becaused by the fact that function restoration processing is initiated bythe user who has operated the function restoration key 30 by mistakealthough function restoration is not required.

Next, the control unit 20 judges whether the power has been turned on ornot (Step 10), and when the PDP 100 is not powered on, the control unit20 then judges whether the function restoration key 30 has been operatedby the user or not (Step S11). Here, when the user performs an operationto power on the PDP 100 before operating the function restoration key30, the control unit directs the interlock circuit 29 to lock thefunction restoration key 30 so that it cannot be operated (Step S12).This process aims at preventing the occurrence of inconveniences causedby the execution of function restoration processing while the PDP 100 isin the power on state. Possible inconveniences are described later.After this, the control unit 20 returns to Step 57, and repeatedlyperforms the control processes of Steps S7 to S12, after causing thedisplay control circuit 18 to present a screen display that prompts theuser to operate the function restoration key 30.

Meanwhile, when judging that the function restoration key 30 has beenoperated while the PDP 100 is in the power off state (Step S1), thecontrol unit 20, after a certain lapse of time, directs the heatingelement energization circuit 23 to energize each of the heating elements11 and causes the timer circuit 24 to start a time measuring operation(Step S13). Accordingly, the energized heating elements 11 generateheat, which is transferred to the phosphor layers 13 through thedielectric layer 9 and the barrier ribs 12. Accordingly, the phosphorlayers 13 are heated. By heating the phosphor layers 13, it becomespossible to improve crystallinity that has been lowered after theexposure to UV light for a certain accumulated time, and therefore torestore its wavelength and luminance to the original state. A mechanismfor restoring the wavelength and luminance of the phosphor layers 13 byheating them in the above manner is the same as a process of restoringcrystallinity by means of annealing that is often used for othermaterials too.

Here, by heating the phosphor layers 13 at a temperature in the range of400° C. to 800° C., preferably 500° C. to 600° C. as a predeterminedheating temperature, it is possible to achieve a favorable effect ofwavelength and luminance restoration. Therefore, the heating elementenergization circuit 23 energizes the heating elements 11 so that thephosphor layers 13 are heated at a temperature within the above range.However, there occurs a temperature gradient between the temperature ofheat generated by the heating elements 11 and the temperature at whichthe phosphor layers 13 are heated because there exist the dielectriclayer 9 and the barrier ribs 12 therebetween. Therefore, the temperatureof heat generated by the heating elements 11 needs to be set inconsideration of such temperature gradient. For example, when theheating temperature of the phosphor layers 13 is set to 500° C., thetemperature of the heating elements 11 should be set to 600° C. In thiscase, since the heat insulation material 17 is provided on the othersurface of the rear glass substrate 8, the temperature of the outersurface of the heat insulation material 17 is reduced to 100° C. orlower. Thus, there is no fear that the user burns his/her hands or thatelectric components attached near the PDP 100 are degraded because ofthe heat.

Furthermore, it is preferable to set the heating time of the phosphorlayers 13 at the above heating temperature to be in the range between 10and 120 minutes inclusive, and more preferably in the range between 20and 60 minutes inclusive. This is because heating of less than 10minutes is not sufficient to restore the wavelength and luminance of thephosphor layers 13, whereas heating of over 60 minutes needlesslyconsumes electric power. Note that “heating time” here refers to alength of time during which the temperature of the phosphor layers 13remains at the above target heating temperature after the temperature ofthe phosphor layers 13 reaches such target heating temperature, ratherthan the time from when the heating of the phosphor 13 starts to whenthe temperature of the phosphor layers 13 returns to ordinarytemperature. In Step S13, therefore, the heating elements 11 startsbeing energized after a certain lapse of time that is required by therespective constituent elements of the PDP 100 to go back to ordinarytemperature after the power is turned off.

Moreover, after directing the heating element energization circuit 23 toenergize the heating elements 11 (Step S13), the control unit 20monitors whether the above predetermined heating time has elapsed or noton the basis of the time measured by the timer circuit 24 (Step S14),while continuously monitoring if the user will not perform an operationto turn on the power by mistake (Step S15). If the user turns the poweron while function restoration processing of the phosphor layers 13 iscarried out, the PDP 100 moves to driven state, making it impossible forthe function restoration processing of the phosphor layers 13 to beperformed correctly. For the same reason, the interlock circuit 29 locksthe function restoration key 30 when the power is on so that the key 30will not be operated.

Upon judging that the power of the PDP 100 has been turned on while thefunction restoration processing of the phosphor layers 13 is takingplace (Step S15), the control unit 20 directs the heating elementenergization circuit 23 to suspend the energization of the heatingelements 11 and directs the interlock circuit 29 to lock the functionrestoration key 30 so that it will not be operated (Step S16).Furthermore, after resetting the time measuring operation of the timercircuit 24 (Step S17), the control unit 20 returns to Step S7 torepeatedly perform the control processes of the above Steps S7 to S15.

Meanwhile, when judging that a predetermined heating time has elapsedafter the start of the function restoration processing of the phosphorlayers 13 (Step S14), the control unit 20 directs the heating elementenergization circuit 23 to stop energizing the heating elements 11 anddirects the interlock circuit 29 to lock the function restoration key 30so that it will not be operated (Step S18), as well as deleting thecontents stored in the memory 27 (Step S19) to complete the functionrestoration processing of the phosphor layers 13.

Note that in the present embodiment, an example case has beenillustrated where the heating elements 11 are provided for therespective phosphor layers 13 of red, blue, and green colors, but it isalso possible to achieve an effect equivalent to the above describedeffect if heating elements 11 are provided only near the blue phosphorlayers 13. This is because wavelength shift and luminance degradationare especially notable in blue phosphor layers 13, while wavelengthshift and luminance degradation of red and green phosphor layers 13 aresmall.

Next, referring to FIGS. 6A, 6B, and 6C, a description is given of amethod for fabricating the PDP 100 according to the present embodiment.First, referring to FIG. 6A, a description is given of processing offabricating a front structure. After forming an Indium Tin Oxide (ITO)film on the cleansed front glass substrate 1 by a sputtering method,transparent electrodes 2 a and 3 a are formed by removing unnecessaryparts using a known photo-etching method (Step 20). Then, bus electrodes2 b and 3 b are formed on these transparent electrodes 2 a and 3 b bymeans of a printing method that uses screen or by a photo-etchingmethod, for example (Step S21).

Next, after forming a light-shielding layer 5 between each of thedischarge electrodes 4 formed on the front glass substrate 1, eachdischarge electrode 4 being comprised of transparent electrodes 2 a and3 a and bus electrodes 2 b and 3 b, paste made from glass powder isapplied all over the front glass substrate 1 by means of printing, forexample. Then, the front glass substrate 1 is heated at around 600° C.to allow the glass powder layer to melt, as a result of which atransparent dielectric layer 6 is formed (Step S22). Finally, aprotective film 7 made of magnesium oxide is formed on the dielectriclayer 6 by a vacuum evaporation method (Step S23), and the fabricationof the front structure is completed.

Next, referring to FIG. 6B, a description is given of processing offabricating the rear structure. First, address electrodes 10 are formedon the cleansed rear glass substrate 8 into a predetermined pattern byusing a thick-film printing method utilizing silver paste (Step S24).Subsequently, processes of fabricating heating elements 11 of Steps S25to S28 are performed. More specifically, using a dispenser or the like,paste, which is obtained by mixing glass powder with a powderyhigh-resistivity material (e.g. stainless, nichrome, tungsten,molybdenum) and then by mixing the resulting powder with a solvent, isapplied between each of the address electrodes 10 on the rear glasssubstrate 8 (Step S25). After this, such applied paste is patterned intolines, each with a width of 50 μm to 100 μm (Step S26), dried (StepS27), and then burnt (Step S28). Accordingly, the glass componentsincluded in the paste melt to serve as glue with which glasses arecoupled onto the rear glass substrate 8, and the high-resistivitymaterial is fixed onto the outer surface of the rear glass substrate 8,allowing a predetermined pattern of heating elements 11 to be formed.

Next, after applying, by means of printing or the like, paste made fromglass powder all over the rear glass substrate 8 on which the addresselectrodes 10 and heating elements 11 have been formed, the rear glasssubstrate 8 is heated at around 600° C. to allow the glass power layerto melt and a transparent dielectric layer 9 to be formed (Step S29).Then, by performing overlay printing by repeating thick-film printingthat uses low melting glasses and drying, glass powder ribs are formed,which are then burnt to form barrier ribs 12 (Step S30). Furthermore, onthe dielectric layer 9 and the barrier ribs 12, phosphor layers 13 thatare colored into red, green, and blue are formed in the respectivedischarge cells 14 by means of thick-film printing (Step S31). Finally,a sealing layer serving as a vacuum sealer is formed around the rearglass substrate 8 by a printing method, and the fabrication of the rearstructure is completed.

Next, referring to FIG. 6C, a description is given of processing ofassembling the front structure and the rear structure. The frontstructure as the front glass substrate 1 and the rear structure as therear glass substrate 8 fabricated through the above-described processesare assembled at mutually opposing positions and tentatively fixed insuch position (Step S32).

Then, a sealing/evacuation/gas filling process (Step S33) is performed.In this process, a chip tube for taking discharge gas to inside isformed on an air exist of the rear glass substrate 8, and then the twosubstrates are burnt in a calcining furnace for sealing. Accordingly,the seal glass in the low-melting sealing layer formed in the finalprocess of fabricating the rear structure and the seal glass of the chiptube melt and weld the two glass substrates 1 and 8 and the exhaust tubetogether. As a result, one panel is formed. As gas filling, the exhausttube gets connected to a vacuum device so as to exhaust the gas insidethe panel in a high-temperature atmosphere that is set at around 400° C.in the high-temperature calcining furnace. Then, by filling the panelwith discharge gas (e.g. a mixture of neon and xenon), the fabricationof a required PDP 100 completes. Finally, an aging process is performedin which voltage that is higher than the breakdown voltage is applied toall the discharge electrodes 4 of the completed panel 100 to performlong-time discharge (Step S34). This process aims at further stabilizingdischarge characteristics.

This fabrication method is realized by adding the processes offabricating heating elements 11 (Steps S25 to S28) to the existingprocesses, and thus such processes of fabricating the heating elements11 may be performed prior to the process of fabricating addresselectrodes 10 (Step S24). In other words, since heating elements 11 canbe successively formed in the same fabrication process as that ofaddress electrodes 10, it is possible to form heating elements 11through simple fabrication processes. As a result, the present methoddoes not require high fabrication cost compared with the existingfabrication methods.

FIGS. 7A, 7B, and 7C are diagrams showing preferable forming patterns ofheating elements 11. FIG. 7A shows that heating elements 11 are formedlike a ladder by arranging linear heating elements 11 in parallel witheach other and commonly connecting the both ends of each heating element11 to lead them to joining terminals 01 and 02. FIG. 7B shows thatheating elements 11 are formed in a zigzag pattern by arranging linearheating elements 11 in parallel with each other, serially connecting theheating elements 11, and leading the both ends of such serial connectionto joining terminals 01 and 02, respectively. The heating elements 11that are formed according to the patterns shown in FIGS. 7A and 7B canbe supplied with power from the heating element energization circuit 23shown in FIG. 4 to be energized. FIG. 7C shows that heating elements 11are formed independently of each other by simply arranging them inparallel with each other without leading them to joining terminals 01and 02. Each of these heating elements 11 is one to which radiofrequencies and microwaves are radiated from outside, by providing ahigh-frequency field generation unit or the like instead of the heatingelement energization circuit 23 shown in FIG. 4, in order to make theheating elements 11 generate heat by themselves by means of inductionheating. Note that it is preferable that top seven and bottom sevenconnection points illustrated in FIG. 7A serve as low-voltage resistorsthat prevent voltage effects in a lateral direction in the drawing.

FIG. 8 is a cross-sectional diagram showing a plasma display panel 101according to the second embodiment of the present invention. Thiscross-sectional diagram shows the PDP 101 that is cut at a positioncorresponding to the A-A line shown in FIG. 1. In this drawing,consistent elements that are the same as or equivalent to those shown inFIG. 2 are assigned the same reference numbers, and descriptions thereofare omitted. While heating elements 11 are provided between each twoneighboring address electrodes 10 in the first embodiment, heatingelements 11 of the PDP 101 of the present embodiment are embedded in thedielectric layer 9, facing the respective address electrodes 10 acrossthe dielectric layer. The other constituent elements are the same asthose presented in the first embodiment.

As is obvious from a comparison between FIG. 2 and FIG. 8, since theheating elements 11 in the PDP 101 are placed closer to the phosphorlayers 13 than those of the PDP 100 of the first embodiment, it ispossible to transfer the heat generated by the heating elements 11efficiently to the phosphor layers 13, which are then heated efficientlyas a result. This makes it possible to achieve the effect that thephosphor layers 13 are heated at a predetermined temperature, whilesetting the heat temperature of the heating elements 11 to lowercompared with the first embodiment. Note that the heating elements 11are energized by the control unit 20 executing the control processingbased on the flowchart shown in FIG. 5.

FIG. 9 is a cross-sectional diagram showing a plasma display panel 102according to the third embodiment of the present invention. Thiscross-sectional diagram shows the PDP 102 that is cut at a positioncorresponding to the A-A line shown in FIG. 1. In this drawing,consistent elements that are the same as or equivalent to those shown inFIG. 2 are assigned the same reference numbers, and descriptions thereofare omitted. While heating elements 11 are provided between each of theaddress electrodes 10 in the first embodiment, plural steps (three stepsin the present embodiment) of heating elements 11, which are placed witha gap between each of them and which are embedded in the barrier ribs12, are in the PDP 102 of the present embodiment. The other constructionis the same as that of the first embodiment.

In this PDP 102, since plural steps of heating elements 11 are placedcloser to the phosphor layers 13 than those of the PDPs 100 and 101 ofthe first and second embodiments, it is possible to transfer the heatgenerated by the heating elements 11 in an extremely efficient mannerand therefore to heat the phosphor layers 13 efficiently. This makes itpossible to achieve the effect that the phosphor layers 13 are heated ata predetermined temperature, while setting the heat temperature of theheating elements 11 to further lower than in the case of the secondembodiment. Here, the heating elements 11 are energized by the controlunit 20 executing the control processing on the basis of the flowchartshown in FIG. 5. Note that a part or the whole of the respective barrierribs 12 may be made of high-resistivity material so that power isapplied to each portion made of high-resistivity material, rather thanembedding the heating elements 11 in the barrier ribs 12. With thisconstruction, the barrier ribs 12 serve also as heating elements. Inthis case, it is possible to heat the phosphor layers 13 in a moreefficient manner.

FIG. 10 is a flowchart showing processing of fabricating the rearstructure of the PDP 101 illustrated in FIG. 8 according to the secondembodiment. First, address electrodes 10 are formed on the cleansed rearglass substrate 8 into a predetermined pattern by using a thick-filmprinting method that utilizes silver paste (Step S35). Subsequently, bymeans of printing or the like, paste made from glass powder is appliedall over the rear glass substrate 8 on which the address electrodes 10have been formed. Then, the front glass substrate 8 is heated at around600° C. to allow the glass powder layer to melt, as a result of which atransparent rear dielectric layer 9 a that is thick enough to cover theaddress electrodes 10 is formed (Step S36).

Next, photosensitive paste including a high-resistivity material isformed to be applied over an upper surface of each address electrode 10on the rear dielectric layer 9 a (Step S37). Then, by forming suchapplied photosensitive paste into a predetermined pattern throughexposure and development processes (Step S38), heating elements 11 areformed. Then, a transparent front dielectric layer 9 b is formed througha process equivalent to Step S36 described above in a manner that thefirst and second dielectric layer 9 a and 9 b can form a dielectriclayer 9 having a predetermined thickness as a whole (Step S39).

Then, by performing overlay printing by repeating thick-film printingthat uses low melting glasses and drying, glass power ribs are formed,which are then burnt to form barrier ribs 12 (Step S40). Furthermore, onthe dielectric layer 9 and the barrier ribs 12, phosphor layers 13 thatare colored into red, green, and blue are formed in the respectivedischarge cells 14 by means of thick-film printing (Step S41). Finally,a sealing layer serving as a vacuum sealer is formed around the rearglass substrate 8 by a printing method, and the processing offabricating the rear structure is completed. Note that the processing offabricating the front structure and the processing of assembling thefront structure and the rear structure are the same as those shown inFIGS. 6A and 6C.

While the present fabrication method involves two processes for formingthe dielectric layer 9 compared with the processing shown in FIG. 6 ofthe first embodiment, there is an advantage that the heating elements 11can be placed closer to the phosphor layers 13 than in the case of thePDP 100 of the first embodiment. Note that the heating elements 11 maybe formed through each of the processes of Steps S25 to S28 shown inFIG. 6B of the first embodiment, rather than through each of theprocesses of Steps S37 and S38 shown in FIG. 10. Furthermore, theheating elements 11 may also be formed through the known fabricationprocesses that are the same as those for fabricating rear glasses ofautomobiles.

Moreover, while no diagrammatic illustration is given for processing offabricating the rear structure of the PDP 102 shown in FIG. 9 accordingto the third embodiment, it is possible to form, through the followingprocedure, a construction in which plural steps of heating elements 11with a gap between them are embedded in the barrier ribs 12: formingaddress electrodes 10 and a dielectric layer 9 on the rear glasssubstrate 8 through processes equivalent to Steps S24 and S29 shown inFIG. 6B; and then repeatedly and alternately performing the process ofStep S30 shown in FIG. 6B for forming the barrier ribs 12 and theprocesses of Steps S25 to S28 shown in FIG. 6B or the processes of StepsS37 and S38 for forming the heating elements 11.

In the first or third embodiment, by the control unit 20 shown in FIG. 1executing the control processing based on the flowchart of FIG. 5, ascreen display is presented to prompt the user to perform the functionrestoration operation and the user then initiates processing of functionrestoration by manually operating the function restoration key 30 basedon such display screen. In addition to this construction, the controlunit 20 may also perform function restoration processing automaticallyupon judging that the PDP is in need of function restoration. FIG. 11 isa flowchart showing control processing performed by the control unit 20when it automatically performs function restoration processing. Thefollowing describes such control processing shown in FIG. 11. Note thatreference numbers of the constituent elements shown in FIG. 4 arereferred to when explaining FIG. 11. However, in the control processingshown in FIG. 11, the function restoration key shown in FIG. 4 is notrequired, and the interlock circuit 29 locks the power key instead sothat it will not be operated. Furthermore, a clock circuit isadditionally required for this control processing.

The control unit 20 continuously monitors whether the power of the PDPis on or not based on the presence/absence of a power-on signal inputtedfrom the power detection circuit 28 (Step S42). Every time there is aninput of power-on signal from the power detection circuit 28, thecontrol unit 20 causes the timer circuit 24 to start its operation (StepS43). Then, the control unit 20 monitors if a power-on signal will stopbeing inputted from the power detection circuit 28 as a result ofterminating the drive of the PDP (Step S44). When judging that the PDPis powered off and no power-on signal is inputted any more, the controlunit 20 obtains a new total drive time by adding the total drive timeread from the memory 27 to the drive time measured by the timer circuit24 (Step S45), and judges whether such obtained total drive time exceedsa predetermined time or not (Step S46). Here, as the predetermined time,2000 to 3000 hours is set after which processing for restoring thedisplay function is required to be performed.

When judging that the predetermined time is not exceeded, the controlunit 20 updates the memory 27 by storing a newly obtained total drivetime (Step S47), after which the control unit 20 returns to Step S42 andrepeats the above control processing. Meanwhile, when judging tht thepredetermined time is exceeded (Step S46), the control unit 20 directsthe display control circuit 18 to present a screen display indicatingthat function restoration processing is to be performed (Step S48).Accordingly, the display screen shows a message saying, for example, asfollows: “Display function restoration processing starts after the poweris turned off. Note that you cannot turn on the power until five nextmorning”.

Then, the control unit 20 monitors if a predetermined processing starttime is reached, with reference to a time signal from the clock circuit(Step S49). Here, the processing start time is set in advance within thetime period during which the user has the least possibility to turn thepower on (e.g. from two to four in the morning) or in the time periodduring which the PDP is not used, the time period being detected by thecontrol unit 20 from a certain length of time starting from when the PDPuse starts.

When judging that the processing start time is reached (Step S49), thecontrol unit 20 judges whether the power is turned off or not based onthe presence/absence of a power-on signal from the power detectioncircuit 28 (Step S50). If the power is turned on, the control unit 20causes the display control circuit 18 to present a screen display thatprompts the user to turn the power off, such as “When the power getsturned off, display function restoration processing is initiated” (StepS51) and then waits for the user to turn the power off.

When judging that the power has been turned off, the control unit 20directs the interlock circuit 29 to lock the power key so that it cannotbe turned on (Step S52), as well as directing the heating elementenergization circuit 23 to energize each of the heating elements 11 andcauses the timer circuit 24 to start time measuring operation (StepS53). Accordingly, the energized heating elements 11 generate heat,which is transferred to the phosphor layers 13 to heat them. Then, thecontrol unit 20 monitors whether a predetermined heating time haselapsed or not on the basis of the time measured by the timer circuit 24(Step S54). Here, a heating temperature and a heating time of theheating elements 11 are set equivalently to those of the firstembodiment.

When judging that a predetermined heating time has elapsed since thefunction restoration processing of the phosphor layers 13 started, thecontrol unit 20 directs the heating element energization circuit 23 tostop energizing the heating elements 11 as well as directing theinterlock circuit 29 to unlock the power key (Step S55), and deletes thecontents stored in the memory 27 (Step S56) to complete the functionrestoration processing of the phosphor layers 13. Accordingly, thecrystallinity of the phosphor layers 13 is improved and their wavelengthand luminance are restored to the original state.

The first and third embodiments have a configuration in which theheating elements 11 are provided, and display function restorationprocessing is performed by energizing the heating elements 11 when atotal drive time reaches a predetermined time so as to heat the phosphorlayers 13. However, it is also possible to cause a conventional PDP toperform display function restoration processing if such conventional PDPdoes not have a mechanism for restoring display function. Next,referring to a flowchart shown in FIG. 12, a description is given of afirst method for restoring the function of a PDP according to thepresent invention.

Before explaining FIG. 12, a description is given of a PDP. In additionto the conventional constituent elements, the PDP is equipped with thepower detection circuit 28, the timer circuit 24, the memory 27, and thecontrol unit 20 that are shown in FIG. 4. As in the case of the first orthird embodiment, the control unit 20 (i) causes the timer circuit 24 totime a length of time during which a power-on signal is inputted fromthe power detection circuit 28, (ii) performs a calculation for addingthe length of time measured by the timer circuit 24 so as to obtain atotal drive time, (iii) causes the memory 27 to store a total drive timeevery time a total drive time is updated, and (iv) continuously monitorswhether the total drive time has reached a predetermined time or not.Furthermore, upon judging that the above predetermined time has beenreached, the control unit 20 gives a direction that a screen displayshould be presented to prompt the user to request the manufacturer ofthe PDP to perform function restoration processing. For example, thescreen display says as follows: “Display function restoration processingis required now. Contact the store where you purchased it”.

The manufacturer, after receiving a notification from the user who hascontacted it as prompted by the above screen display, collects the PDPand removes the discharge gas (e.g. a mixture of neon and xenon) fromsuch collected PDP (Step S57). Then, the manufacturer puts the PDP intothe heating furnace to heat it at a predetermined heating temperaturefor a predetermined period of time, while exhausting air from theinternal spaces from which the discharge gas has been removed (StepS58). The heating temperature and heating time are as described in thefirst or third embodiment. Through this heating processing, thecrystallinity of the phosphor layers 13 that has become lowered afterthe exposure to UV radiation for a certain accumulated time is improvedand their wavelength and luminance are restored to the original state.After this heating processing for restoring display function, themanufacturer fills the PDP with discharge gas to return it to theoriginal state (Step S59). Finally, the manufacturer performs an agingprocess in which voltage that is higher than the breakdown voltage isapplied to all the discharge electrodes 4 of the completed panel toperform long-time discharge (Step S60).

This method for restoring the function of a PDP is capable of draining,to outside, impurities that are generated inside the internal spaces atthe time of heating, since discharge gas is removed from the PDP priorto heating, and air is exhausted, while the PDP is heated, from theinternal spaces from which discharge gas has been drained. Accordingly,since it is possible to prevent the occurrence of adverse effects causedby the fact that the impurities vaporized by heating react with thephosphor layers 13, it becomes possible to restore the display functionin a further efficient manner. What is more, since the PDP is heated ina heating furnace according to the present restoration method, notemperature gradient occurs across the area from the vicinity of theheating elements to the phosphor layers 13, in the case where theheating elements 11 are provided as described above. Accordingly, it ispossible to heat the phosphor layers 13 correctly at a heatingtemperature that is set to the heating furnace and therefore to performa desirable function restoration processing. Note that the same functionrestoration effect can be achieved if the collected PDP is inserteddirectly into the heating furnace for heating, without performing theabove gas exchange.

FIG. 13 is a schematic diagram showing a second method for restoring thefunction of a PDP according to the present invention. As in the case ofthe PDP presented for the explanation of the first restoration methodshown in FIG. 12, a PDP 110 according to this embodiment is equippedwith the power detection circuit 28, the timer circuit 24, the memory27, and the control unit 20 shown in FIG. 4, without including anyheating elements and energization units. In other words, in the presentrestoration method, as in the case of the first restoration method shownin FIG. 12, the manufacturer collects the PDP 110 when receiving anotification from the user who has contacted it as prompted by the abovescreen display, but it restores the function of the phosphor layers byheating them by use of a photoirradiation unit, rather than throughheating processing utilizing the heating units as in the case of thefirst restoration method.

Referring to FIG. 13, the present embodiment uses, as a photoirradiationunit, a photoirradiation apparatus 31 that is comprised of a pluralityof xenon flash lamps 32 that are placed in parallel with each other. Byflashing each of such xenon flash lamps 32 in synchronization with alamp drive circuit 33, lights L are irradiated to the PDP 110. Then, byirradiating such lights L to the outer surface of the phosphor layers 13via the glass substrate 1, dielectric layer 6, and protective film 7shown in FIG. 1, the surface of the phosphor layers 13 are heated at400° C. to 800° C.

In the present embodiment, an example case is presented in which thelights L are directly irradiated to the PDP 110 without disassemblingit. In this case, in order to heat the phosphor layers 13 at theabove-described temperature, a condition needs to be set as follows: asa xenon flash lamp 32, a lamp that emits a light L with wavelengths inthe range between 200 nm and 4.5 μm inclusive should be selected. Thisis because the use of a light L with a wavelength of 4.5 μm or lessmakes it possible for the light L to reliably reach the phosphor layers13 via the glass substrate 1, dielectric layer 6, and protective film 7,whereas the reason for using a light L with a wavelength of 200 nm ormore is because a light L with a wavelength of 200 nm or less mightdestroy the phosphor crystallinity of the phosphor layers 13. Note thatit is more preferable to use an infrared radiation with a wavelength of800 nm or more since it is conceivable that a visible light's highreflectivity and transmittance from and to the phosphor layers 13hinders the heating from being performed in an efficient manner.

Meanwhile, the drive control unit 34 controls the power supply from thelamp drive circuit 33 to the xenon flash lamps 32 so that each of thexenon flash lamps 32 emits a light L with energy densities in the rangebetween 100J/cm² and 5000J/cm² inclusive. This is because the energydensity of 100J/cm² or less is not enough for heating, whereas theenergy density of 5000J/cm² or more is too high since luminancerestoration of the phosphor layers 13 becomes saturated, resulting in awaste of energy.

Furthermore, the drive control unit 34 controls a length of time forwhich the photoirradiation apparatus 31 comprised of a plurality ofxenon flash lights 32 remains driven to irradiate lights L, to anextremely short time such as in the range between 1 nsec and 10 msecinclusive. This is because it is technically difficult to drive eachxenon flash lamp 32 to make it flash for an extremely short time of 1nsec or less and it is costly even if it is possible. Meanwhile, if eachxenon flash lamp 32 is driven for 10 msec or more, heat is transferredfurther than the outer surface of the phosphor layers 13, andrestoration processing is performed also for phosphor particles that arenot suffering from serious degradation, resulting in a waste ofprocessing energy and processing time. Furthermore, there also occursthe possibility that constituent elements of the PDP 110 become crackedby thermal shock because thermal expansion coefficients are different onan element-by-element basis, and that defects such as the coming off offilms and quality degradation occur due to the fact that the constituentelements other than the phosphor layers 13 are adversely affectedbecause thermal expansion coefficients are different for eachconstituent element.

Note that in the case where the collected PDP 110 is disassembled andlights L are directly irradiated to the phosphor layers 13, there is noneed to set the above conditions concerning the wavelength and energydensity of each light L and concerning a length of time during whichlights L should be irradiated. In this case, however, processes ofdisassembling and reassembling the PDP 110 are required.

In such case where the lights L are directly irradiated to the phosphorlayers 13, there is an advantage that only a least possible processingenergy as well as a shorter processing time is required since only theoutermost surface of each phosphor layer 13 suffering from the mostserious degradation is heated. Furthermore, since a processing time isextremely short, there is no thermal shock on the PDP 110, which causesno possibility that the constituent elements other than the phosphorlayers 13 become subject to the coming off of films and qualitydegradation.

Note that phosphor particles, which can be restored by the irradiationof lights L, emit lights according to the following mechanism: theirparent body or parent crystal such as BAM absorb energy from outside;the absorbed energy is then transferred to luminescent ions; the ions inthe ground state move to the excited state; the excited ions reach theluminescence level that is a more stable excited state, while losingenergy due to thermal/lattice vibration; and the excited ions return tothe ground state, emitting lights.

FIG. 14 is a schematic diagram showing another example of the secondmethod for restoring the function of a PDP according to the presentinvention. In this example, laser beams are used as lights L to beirradiated. More specifically, laser beams emitted from an excimer laserapparatus 37 are irradiated to the PDP 110, with their linear beam shapemaintained using an optical system. A stage 39, on which the PDP 110 isfixedly mounted, moves in directions indicated by arrows so that laserbeams L are irradiated all over the PDP 110. The same effect asdescribed in FIG. 13 is achieved through the use of the laser beams L.

FIG. 15 is a schematic diagram showing a third method for restoring thefunction of a PDP according to the present invention. The presentembodiment requires a condition that phosphor layers of a PDP 111 shouldbe composed of phosphor particles to which conductive particles whoseelectric resistivity is in the range between 8 μΩcm and 200 μΩcminclusive are mixed at a predetermined ratio. Here, conductive particlesare mixed in a ratio of 0.1 (wt %) to 10 (wt %) with regard to the wholephosphor layers. Moreover, it is preferable to use iron, nickel, orchromium as conductivity particles. Furthermore, the PDP 111 is equippedwith the power detection circuit 28, the timer circuit 24, the memory27, and the control unit 20 shown in FIG. 4, as in the case of the PDP110 used in the second restoration method.

In this restoration method, as in the case of the above-described secondrestoration method, a manufacturer collects the PDP 111, when receivinga notification from its user who has contacted such manufacturer asprompted by the screen display, and inductively heats the conductiveparticles mixed in the phosphor layers by applying a high-frequencyelectric field to the PDP 111. Accordingly, the phosphor layers areheated and their functions are restored. More specifically, as FIG. 15shows, the collected PDP 111 is placed onto a tubular base frame 40.Then, by applying high-frequency power from a high-frequency powersupplier 42 to spiral heating coils 41 such as IH coils that are placedbelow the base frame 40, the heating coils 41 generate electromagneticwaves by which a high-frequency electric field is applied to thephosphor layers of the PDP. Accordingly, the conductive particlesincluded in such phosphor layers are inductively heated and generateeddy currents. The phosphor particles included in the phosphor layersare heated by Joule heat caused by such eddy currents, as a result ofwhich the function of the phosphor layers is improved.

Conductive particles are mixed to the phosphor layers with a mixingratio of 0.1 (wt %) to 10 (wt %), as described above. This is because amixing ratio of 0.1 (wt %) or less is not enough to inductively heat thePDP 111 and therefore a function restoration of the phosphor layerscannot be performed as desired, whereas a mixing ratio of 10 (wt %) orover leads to a reduction in the number of phosphor particles includedin the phosphor layers and therefore the phosphor layers cannot achievedesired luminance.

Furthermore, as conductive particles to be mixed into the phosphorlayers, it is preferable to use ones whose electric resistivity is inthe range between 8 μΩcm and 200 μΩcm inclusive, as described above.This is because an electric resistivity of 8 μΩcm or less is too low andonly a small amount of Joule heat is generated, whereas an electricresistivity of 200 μΩcm or over causes too small induced currents andonly a small amount of Joule heat is generated. In other words, thephosphor layers cannot be heated sufficiently in either case.

Furthermore, the high-frequency power supplier 42 supplies, under thecontrol of a controller 43, the heating coils 41 with high-frequencypower with which it is possible to apply, to the conductive particlesincluded in the phosphor layers, a high-frequency electric field that isin the range between 10V/cm and 300V/cm inclusive. This is because theapplication of a high-frequency electric field of 10V/cm or less resultsin too small induced current and only a small amount of Joule heat isgenerated, as a result of which the phosphor layers cannot be heatedsufficiently. Meanwhile, the application of a high-frequency electricfield of 300V/cm or over is too high and there is a possibility thatother constituent elements mounted on the PDP 111 will be damaged.

As the high-frequency power supplier 42, a high-frequency power supplieris selected that applies a high-frequency electric field in thefrequency range between 1 KHz and 3 GHz inclusive to the conductiveparticles included in the phosphor layers. This is because sufficientinduction heating cannot be carried out if the frequency of ahigh-frequency electric field is 1 KHz or lower, whereas ahigh-frequency power supplier that generates a high-frequency electricfield in the frequency range of 3 GHz or higher is costly.

In the above-described function restoration method in which the phosphorlayers are heated by inductively heating the conductive particles mixedinto the phosphor layers through the application of a high-frequencyelectric field to the phosphor layers, there is an advantage that only aleast possible processing energy as well as a shorter processing time isrequired since only the phosphor layers are heated locally, as in thecase of the second restoration method in which lights are irradiated.Furthermore, since a processing time is extremely short, there is nothermal shock on the PDP 111, which causes no possibility that theconstituent elements other than the phosphor layers become subject todefects such as the coming off of films and quality degradation. What ismore, in addition to this effect, this third restoration method requiresonly an inexpensive electromagnetic field generation apparatus, whilethe second restoration method, in which lights are irradiated, requiresexpensive apparatuses such as the xenon flash lamps 32 and excimer laserapparatus 37. Therefore, the third restoration method is applicable, forexample, to IH cooking equipments for household use or larger IH cookingequipments for industrial use, which produces the effect that there isno cost overrun FIG. 16 is a schematic diagram showing a fourth methodfor restoring the function of a PDP according to the present invention.The fourth restoration method, which is a variation of the thirdrestoration method, is different from the third restoration method onlyin that, instead of conductive particles that are mixed to the phosphorlayers in the third restoration method, phosphor layers of a PDP 112 arecomposed of phosphor particles to which dielectric particles are mixedin a predetermined ratio, the dielectric particles being made ofdielectric materials whose dielectric loss factor fall within the rangebetween 0.01 and 0.6 inclusive when the frequency of a high-frequencyelectric field to be applied is in the range between 1 KHz to 3 GHz.

The dielectric particles are mixed in a ratio of 0.1 (wt %) to 10 (wt %)with regard to the whole phosphor layers, as in the case of theconductive particles in the third restoration method. As dielectricparticles, it is preferable to use dielectric particles whose dielectricloss factor is high and which are highly heat-resistant. For example,lead zirconate titanate is a highly preferable dielectric particle to bemixed to phosphor particles since its dielectric loss factor is 0.04 andit has heat resistance up to 500° C. or over.

Furthermore, the PDP 112 is equipped with the power detection circuit28, the timer circuit 24, the memory 27, and the control unit 20 shownin FIG. 4, as in the case of the PDPs 100, 110, and 111 used in thefirst or third restoration method.

In the fourth restoration method, as in the case of the above-describedthird restoration method, a manufacturer collects the PDP 112, whenreceiving a notification from its user who has contacted suchmanufacturer as promoted by the screen display, and as FIG. 16 shows,places the collected PDP 112 onto a support table 44 made of dielectricmaterial. Then, by applying high-frequency power from the high-frequencypower supplier 42 to spiral heating coils 41 that are located under suchsupport table 44, the heating coils 41 generate electromagnetic waves bywhich a high-frequency electric field is applied to the phosphor layersof the PDP 112 via the support table 44. Accordingly, the dielectricparticles included in such phosphor layers are inductively heated andgenerate eddy currents. The phosphor particles included in the phosphorlayers are heated by Joule heat caused by such eddy currents, as aresult of which the function of the phosphor layers is improved.

Dielectric particles are mixed to the phosphor layers with a mixingratio of 0.1 (wt %) to 10 (wt %), as described above. This is because amixing ratio of 0.1 (wt %) or lower is not enough to inductively heatthe PDP 112 and therefore a function restoration of the phosphor layerscannot be performed as desired, whereas a mixing ratio of 10 (wt %) orover leads to a reduction in the number of phosphor particles includedin the phosphor layers and therefore the phosphor layers cannot achievedesired luminance.

Moreover, the dielectric loss factor of dielectric particles to be mixedinto the phosphor layers in relation to the frequency of ahigh-frequency electric field to be applied is in the range between 0.01and 0.6. This is because dielectric loss (heating value) W can berepresented as W=ω×Co×Vo²×ε×tan δ, where “ω” denotes each frequency ofhigh-frequency power, “Co” denotes the capacitance of dielectricparticles, “Vo” denotes voltage to be applied to the dielectricparticles, “ε” denotes the dielectric constant of the dielectricparticles, and “tan δ” denotes the dielectric loss factor of thedielectric particles.

Thus, when the dielectric loss factor is 0.01 or smaller, heating cannotbe performed sufficiently since tan δ in the above expression is toosmall and the amount of heat to be generated becomes small, whereas whenthe dielectric loss factor is 0.6 or larger, accumulated charge ofaddress discharge becomes likely to be dissipated and therefore therearises the possibility that memory effect achieved by address dischargeis lost.

Furthermore, the high-frequency power supplier 42 supplies, under thecontrol of a controller 43, the heating coils 41 with high-frequencypower with which it is possible to apply, to the dielectric particlesincluded in the phosphor layers, a high-frequency electric field that isin the range between 10V/cm and 300V/cm inclusive. This is because theapplication of a high-frequency electric field of 10V/cm or less resultsin too small induced current and only a small amount of Joule heat isgenerated, as a result of which the phosphor layers cannot be heatedsufficiently. Meanwhile, the application of a high-frequency electricfield of 300V/cm or over is too high and there is a possibility thatother constituent elements mounted on the PDP 112 will be damaged.

As the high-frequency power supplier 42, a high-frequency power supplieris selected that applies a high-frequency electric field in thefrequency range between 1 KHz and 3 GHz inclusive to the dielectricparticles included in the phosphor layers. This is because sufficientinduction heating cannot be carried out if the frequency of ahigh-frequency electric field is 1 KHz or lower, whereas ahigh-frequency power supplier that generates a high-frequency electricfield in the frequency range of 3 GHz or higher is costly.

In the above-described function restoration method in which the phosphorlayers are heated by inductively heating the dielectric particles mixedinto the phosphor layers through the application of a high-frequencyelectric field to the phosphor layers, there is an advantage that only aleast possible processing energy as well as a shorter processing time isrequired since only the phosphor layers are heated locally, as in thecase of the second restoration method in which lights are irradiated.Furthermore, since a processing time is extremely short, there is nothermal shock on the PDP 112, which causes no possibility that theconstituent elements other than the phosphor layers become subject todefects such as the coming off of films and quality degradation. What ismore, in addition to this effect, this fourth restoration methodrequires only an inexpensive electromagnetic field generation apparatus,while the second restoration method, in which lights are irradiated,requires expensive apparatuses such as the xenon flash lamps 32 andexcimer laser apparatus 37. Therefore, the fourth restoration method isapplicable, for example, to IH cooking equipments for household use orlarger IH cooking equipments for industrial use, which produces theeffect that there is no cost overrun.

Although only some exemplary embodiments of this invention have beendescribed in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of this invention. Accordingly, all such modifications areintended to be included within the scope of this invention.

1. A method for restoring a function of a plasma display panel (PDP),comprising restoring a function of a PDP by raising a temperature of atleast a phosphor layer in the PDP to 400° C. to 800° C.
 2. The methodfor restoring a function of a PDP according to claim 1, wherein the PDPis equipped with a heating element, and the temperature of at least thephosphor layer in the PDP is raised to 400° C. to 800° C. by energizingthe heating element.
 3. A method for restoring a function of a plasmadisplay panel (PDP), comprising restoring a function of a PDP by raisinga temperature of a phosphor layer in the PDP to 400° C. to 800° C.through irradiation of light to the PDP.
 4. The method for restoring afunction of a PDP according to claim 3, wherein the light is irradiatedto the phosphor layer from outside the PDP through a glass substrate anda dielectric layer in the PDP.
 5. A method for restoring a function of aplasma display panel (PDP), comprising restoring a PDP by raising atemperature of a phosphor layer in the PDP to 400° C. to 800° C. byinductively heating conductive particles through application of ahigh-frequency electric field to the PDP, said conductive particlesbeing mixed, at a predetermined ratio, with phosphor particles that makeup the phosphor layer.
 6. A method for restoring a function of a plasmadisplay panel (PDP), comprising restoring a PDP by raising a temperatureof a phosphor layer in the PDP to 400° C. to 800° C. by inductivelyheating dielectric particles through application of a high-frequencyelectric field to the PDP, said dielectric particles being mixed, at apredetermined ratio, with phosphor particles that make up the phosphorlayer.
 7. A plasma display panel (PDP), comprising a first substrate onwhich discharge electrodes and a first dielectric layer are formed, eachof said discharge electrodes generating a display discharge and saidfirst dielectric layer covering the discharge electrodes; and a secondsubstrate on which the following are formed: address electrodes that arelocated orthogonally to the discharge electrodes; a second dielectriclayer that covers the address electrodes; barrier ribs that are formedon the second dielectric layer; phosphor layers, each being formed in aconcave portion between each two neighboring barrier ribs; and heatingelements that are located close to the respective phosphor layers. 8.The PDP according to claim 7, wherein the heating elements have a linearshape and are formed on the second substrate, each of the heatingelements being located between each two neighboring address electrodesin parallel with said address electrodes and being embedded in thesecond dielectric layer.
 9. The PDP according to claim 7, wherein theheating elements have a linear shape and are located above therespective address electrodes in parallel with said address electrodes,the heating elements being embedded in the second dielectric layer. 10.The PDP according to claim 7, wherein each of the heating elements isformed at least as part of each of the barrier ribs.
 11. The PDPaccording to claim 7, further comprising: a control drive circuit thatcontrols drive of the discharge electrodes and the address electrodes;and a heating element energization circuit that controls energization ofthe heating elements so that said heating elements heat the phosphorlayers at a predetermined temperature for a predetermined time.
 12. ThePDP according to claim 7, further comprising: a timer circuit thatmeasures a panel drive time during which the PDP has been driven; amemory that stores a total drive time that is obtained by accumulatingeach panel drive time measured by the timer circuit, said total drivetime being updated and stored into the memory every time the timercircuit newly measures a panel drive time; a function restoration key bywhich an instruction for energizing the heating element is inputted,said key being operated manually; a heating element energization circuitthat energizes the heating elements when the function restoration key isoperated; and a control unit operable to indicate that an operation ofthe function restoration key should be performed, when judging that thetotal drive time stored in the memory reaches a set time.
 13. The PDPaccording to claim 7, further comprising: a timer circuit that measuresa panel drive time during which the PDP has been driven; a memory thatstores a total drive time that is obtained by accumulating each paneldrive time measured by the timer circuit, said total drive time beingupdated and stored into the memory every time the timer circuit newlymeasures a panel drive time; a heating element energization circuit thatenergizes the heating elements; and a control unit operable to directthe heating element energization circuit to energize the heatingelements when judging that the total drive time stored in the memoryreaches a set time.
 14. The PDP according to claim 13, furthercomprising a clock circuit that provides time information, wherein whena pre-set time is reached, the control unit directs the heating elementenergization circuit to energize the heating elements, based on the timeinformation provided by the clock circuit.
 15. The PDP according toclaim 11, wherein the heating element energization circuit controls theenergization of the heating element so that the phosphor layers areheated at 400° C. to 800° C., preferably 500° C. to 600° C., for 10 to120 minutes, preferably 20 to 60 minutes.